1. Field of the Invention
This invention relates to a fuel injection valve in particular for high-pressure injection of fuel into combustion chambers of internal combustion engines.
2. Description of the Prior Art
In fuel injected internal combustion engines, the fuel is injected from a high-pressure chamber into the combustion chamber by means of a fuel injector in order to produce a mixture. In common rail injection systems, the servo principal among others is used to open and close the injection valves. The injection valve 40 is part of a servo valve. An electrically triggered on-off valve controls a volume flow. By means of a pressure divider, which is comprised of two through flow resistors, an open on-off valve produces an opening motion of the servo valve. A closed on-off valve produces a closing motion of the servo valve.
In order to achieve an optimal combustion process in the combustion chamber, it is necessary to control the time, the duration of injection, the total fuel quantity injected, and the chronological course of the injection rate as precisely as possible since the combustion chamber geometry is precisely adapted to these parameters in order to minimize fuel consumption and exhaust emissions.
The object of the current invention, therefore, is to produce a fuel injection valve with a combination of an on-off valve and a servo-hydraulic valve in which there is a precisely defined through flow resistance of the on-off valve in the greatest possible range of different fuel pressures. Moreover, this through flow resistance must have the property that only a few geometric parameters influence its magnitude. The precisely defined through flow resistance of the on-off valve thereby determines the opening speed of the servo valve.
The fuel injection valve according to the present invention, has the advantage that the effective flow cross section of the opening produced by the on-off valve encourages the formation of a cavitating throttle flow. The eccentric position of the inlet throttle bore causes a rotation of the fuel flow in the control chamber. This rotation which, after the opening of the on-off valve, accelerates as it flows through the outlet throttle bore due to the conservation of momentum in the fuel flow, leads to a reduction of the static pressure in the fluid and thereby increases the cavitation tendency of the fluid as it flows through the outlet throttle bore. As a result of the spin-encumbered flow inside the outlet throttle bore, the cavitation tendency is extended to a wide pressure range. Even with slight pressure differences over the outlet throttle bore and with high pressures in the low-pressure region downstream of the outlet throttle bore, cavitation effects occur and result in the fact that the effective opening cross section, which is constituted by the combination of the solenoid valve 40 and outlet throttle bore 30, is only influenced by the geometry of the outlet throttle bore. As a result of this, an exactly defined through flow cross section can be established with the aid of the size of the outlet throttle bore, without having to take into account the influence of the solenoid valve 40.
According to a preferred embodiment, the inlet throttle bore is aligned tangential to the control chamber. This results in the fact that all regions of the flow in the control chamber are set into rotation.
According to another embodiment, with a cylindrically embodied control chamber, the rotation of the flow is not hindered by edges or corners. Preferably, the inlet throttle bore and the outlet throttle bore are disposed at right angles to each other. As a result, the rotation axis of the flow produced extends parallel to the influx direction of the fuel into the outlet throttle bore.